1. Field of the Invention
The present invention relates to a backlight module which is used in a display, and in particular to a backlight module which is used in a liquid crystal display.
2. Description of Prior Art
Recently, liquid crystal displays (LCDs) are luminesced by adopting planar light sources, such as external electrode fluorescent lamps (EEELs) or cold cathode fluorescent lamps (CCFLs), where the backlight source can completely turn-on or turn-off the EEELs or CCFLs to light all regions of the backlight source. However, the planar light sources can not provide different luminance levels in particular regions.
In order to solve the problem, a local dimming technology of the backlight source has been developed to supply light with partially adjusted brightness to the LCDs, which has advantages of lower power consumption, increased display contract ratio, higher gray scale numbers and reduced dynamic image blur.
For example, while a backlight source supplying for an LCD using 12 CCFLs as a light source, the backlight source controls just the luminance levels corresponding to 12 regions on which the CCFLs located. Moreover, over-frequent turn-on and turn-off rate of the CCFLs will decrease the life-time due to the limited turn-on and turn-off rate of the CCFLs.
On the other hand, a light guide plate is used for a backlight module supplying for a general LCD. The LCD employing the local dimming technology generates light with brightness value adjusted by the light guide plate in order to particularly supply the light to the LCDs. However, the light generated from the backlight source may be guided by the light guide plate to another region adjacent this region, thus reducing the contract ratio of luminance.
Moreover, since the backlight source employing the local dimming technology is composed of a plurality of light guide plates to satisfy the requirement of size or shape of the LCDs, there are caused problem of bright lines (luminescent lines) resulted from seams between the light guide plates, and the contract ratio of luminance may be reduced.